Bolts and nuts are widely used for tightly fixing a member or the like.
However, there is a problem in that the bolts and nuts are loosened when vibrations are repeatedly applied to the tightly fixed part.
Therefore, various devices have been proposed conventionally.
For example, there is proposed a fastening member including a head section, and a tapered section having an inner surface formed into a conical curve surface and an outer surface formed into a concave curve surface (Patent Literature 1).
This fastening member is capable of firmly and tightly fixing an object to be fastened, and absorbing vibrations and shocks due to an action of the tapered section, to thereby attain an excellent locking action.
In the case of such a special shape as in this fastening member, however, only the cutting work using a lathe or the like can manufacture the fastening member without difficulties. Besides, the cutting work requires special skill in manufacture, thus leading to a problem of high cost.
Further, in recent years, there has been demanded a bolt having a further enhanced locking action.